Documentation is a moving target. Depending on your project, you often have to mix background explanations with code samples. Fields evolve. New people show up.

Documentation is a moving target. Depending on your project, you often have to mix background explanations with code samples. Fields evolve. New people show up. Documentation can never really be good enough. Books provide a way of filling in certain gaps in a structured way that gives people more background. Often times, people expect documentation to do more than this. I tend to agree with you, but it's not what end users end up needing a lot of the time.